Helicobacter pylori is a bacterial species found in the human gastric mucosa. The rate of Helicobacter pylori infection is closely related to social and economic factors, tending to be high in developing countries and low in advanced countries. However, the rate of infection among the Japanese is remarkably high among the advanced countries and it is even reported that 80% of people in and after the fourth decade of life have been infected. In recent years, it has been revealed that Helicobacter pylori may cause various gastric and duodenal diseases such as gastric ulcer, duodenal ulcer, chronic gastritis and, further, gastric cancer.
Since it was proven that the possibility of being afflicted by these diseases can be reduced by eradicating Helicobacter pylori, international discussions have been made about the diseases at which Helicobacter pylori eradication is to target. Thus, the diseases currently considered to be targets of such eradication include gastric ulcer, duodenal ulcer, malignant gastric lymphoma, residual stomach after resection due to early gastric cancer.
With the recognition of Helicobacter pylori eradication therapy as a novel method for the treatment of gastric and duodenal diseases, guidelines for therapeutic trials have been laid down and methods for diagnosis about occurrence of Helicobacter pylori infection and judgment about bacterial eradication have been proposed by the Japanese Society of Gastroenterology (The Japanese Journal of Gastroenterology, vol. 96, 199-207, 1999). According to the above guidelines for therapeutic trials, it is indicated that the diagnosis about an occurrence should be carried out based on an invasive test method, namely culture of a biopsy specimen from a gastric site, microscopy and a urease test, and that the judgment about bacterial eradication essentially requires culture of a biopsy specimen from a gastric site and microscopy and a urea breath test, which is a noninvasive test method. In special cases, for example in the case of a pediatric subject, it is indicated that the judgment should be carried out based on the combination of a test for anti-Helicobacter pylori antibodies in blood and the diagnosis about an occurrence.
However, these test methods for Helicobacter pylori infection have the following problems. The invasive test method inflicts a great deal of pain on subjects on the occasions of gastroscope insertion and biopsying. As for the noninvasive test methods, the pain sensation in subjects is markedly reduced but the urea breath test requires fasting prior to the test. Further, in carrying out the urea breath test, such apparatus as a mass spectrometer, an infrared spectrophotometer, etc. are required, hence the test can be carried out only in special institutions, and the resulting high cost is also a drawback. The antibody test is not suited for the judgment about bacterial eradication since the antibody titer in blood remains at high levels for a long term after eradication of the bacteria. Therefore, the advent of a noninvasive test method which may replace the above test methods and by which Helicobacter pylori infection can be detected directly and specifically with high accuracy has been awaited.
In the art, isolation culture of infective bacteria from digestive tract excreta, particularly feces, using a selection medium, has been made as a direct test method for infective bacteria in the digestive tract. As far as Helicobacter pylori is concerned, however, in spite of a large number of trials, there are few reports about the isolation, by culture, from feces. The reason may be considered that this microorganism has already undergone a transformation to the coccoid form, which cannot be culturally isolated, in the lower digestive tract since Helicobacter pylori undergoes, in vitro, a morphological change from the ordinary helical form to the coccoid form, which cannot be cultured, under unfavorable environmental conditions such as low temperature, nutritional deficiency and oxygen deficiency.
On the other hand, as regards direct detection of Helicobacter pylori from feces by an immunological method based on the antigen-antibody reaction, there is a report about the detection of Helicobacter pylori in excreta specimens, such as feces, by an immunoassay using polyclonal antibodies against Helicobacter pylori (J. Clin. Microbiol., vol. 33, 2162-2165, 1995; Japanese Kokai Publication Hei-10-10128 (JP 3043999)).
However, polyclonal antibodies generally have cross reactivity and are inferior in specificity and, in addition, are disadvantageous in that the antibody titer and specificity may vary depending on the lot of antiserum. Therefore, there is a problem that the production of diagnostic tests in which polyclonal antibodies are used is essentially difficult in terms of the quality control. In actuality, as regards the kit “HpSA” for detecting the antigen of Helicobacter pylori in feces, which is a product of Meridian, the patentee of JP No. 3043999, and in which a polyclonal antibody is used, questions about encountered false positive cases and low specificity have been raised (Medical Tribune, 4-5, Jun. 3, 1999 issue; Am. J. Gastroenterol., vol. 94, 1830-1833, 1999).
On the contrary, in Japanese Kokai Publication Hei-10-10128, it is described to the effect that since strains of Helicobacter pylori are susceptible to mutation, monoclonal antibodies capable of reacting only with respective individual antigens are not suited for use in detecting Helicobacter pylori but polyclonal antibodies, which can react with various antigens or epitopes, are rather suited for the detection of Helicobacter pylori. 